According to Bulosan's biography in the link below, he never officially became an American citizen. However, this does not mean that your description of him as an American of Filipino descent is wrong. According to Werner Sollors's study of American ethnic cultures, Beyond Ethnicity. Consent and Descent in American Culture, ethnic writers are caught within two poles, consent and descent. As they move to America, they consent to be American citizens. In the case of Bulosan, this consent can be seen in how he portrays America as a mythic land in America Is in the Heart and how he too subsribes to the quintessentially American pursuit of social mobility. As Bulosan encounters racism and discrimination, he is led to revise his mythic image of America through the lenses of the class, in addition to ethnic, struggle, but the conclusion of his autobiographical novel seems to reassert his faith in America. At the same time, Bulosan is also of Filipino descent as that community was an important point of reference for his life in America. Always aware of his ethnicity, Bulosan became a labor union organizer, campaigning in particular for the rights of immigrants.